Thousands of Georgians signed up for health coverage on the Health Insurance Marketplace last month, although the pace slowed considerably from earlier months.

Nearly 140,000 Georgia consumers have selected a health plan through HealthCare.gov since the marketplace launched Oct. 1, according to new federal data. That’s up nearly 38 percent from enrollment during the site’s first four months of operation, compared with growth of 73 percent in January.

Nationwide, more than 4.2 million Americans have selected plans on the marketplace, a key element of the Affordable Care Act. Federal officials said Tuesday afternoon they don’t know how many of those people have made their first premium payments needed for coverage to actually take effect.

“We expect even more will sign up as we approach the March 31 deadline,” Health and Human Services Secretary Kathleen Sebelius said in a conference call with reporters Tuesday.

Consumers have less than three weeks to buy insurance plans and possibly qualify for federal tax credits on the marketplace before open enrollment closes March 31. Most Americans are required by the Affordable Care Act to have health insurance starting this year or face a tax penalty.

While the number of Georgians signing up for marketplace plans continued to climb in February, the two months prior saw even bigger jumps, in large part because of pent-up demand from people who tried but failed to sign up for coverage through the error-riddled website. Enrollment grew eightfold in December alone once the site finally started working.

Twenty-eight percent of sign-ups so far in Georgia have been among adults age 18 to 34 — the generally healthier “young invincibles” who experts say insurers need to help balance the costs of older, sicker consumers. Nationwide, one in four people signed up are in that age group.

Those numbers are enough to make the marketplace sustainable, although, ideally about one-third of enrollees should be in that younger, healthier category, said William Custer, a health care expert at Georgia State University.

Fifty-eight percent of Georgians who have signed up through the marketplace are women, while 85 percent of people qualified for financial assistance to help lower premium costs. More than 62,000 low-income people also qualify for the state’s Medicaid program, according to the federal data.

Ultimately, predictions of future marketplace enrollment shouldn’t be based on this first year, Custer said. More people will sign up as they learn about coverage options and face increasingly higher penalties for remaining uninsured, he said.

Enrollment growth in February was below expectations but still respectable, he said. “These are workable numbers.”